1. Field of the Invention
The present invention relates to an organic silicone quaternary ammonium salt and the method of producing such an organic silicone compound. In addition, the present invention also relates to a toner and a dry developer comprising the above-mentioned organic silicone quaternary ammonium salt for developing latent electrostatic images.
2. Discussion of Background
The research for synthesis of a variety of organic silicone compounds has been actively made in recent years, and the physical and chemical properties of the thus produced organic silicone compounds have been intensively studied. In particular, special attention has been paid to interesting characteristics of an organic polysilane, that is, a polymeric compound having Si--Si bond, and the application of such a polymer to various fields is now desired. Thus, organic silicone compounds have played a significant role in the field of organic synthesis, and polymeric silicone materials such as silicone resins have been widely utilized.
A silicon atom, which is an element belonging to the same group of a carbon atom in the periodic table of the elements, generally forms a tetravalent compound in the form of tetrahedron. Therefore, the chemical properties, for example, solubility and stability of silicone compounds in an organic solvent are extremely similar to those of carbon compounds.
However, the physical properties of the silicone compounds are different from those of the carbon compounds. For example, the radius of a silicon atom is relatively large than that of a carbon atom, and electronegativity of silicon atom is smaller than that of carbon atom, so that silicon atom is electrically positive. Further, the bond energy between a silicon atom and a hetero atom such as a halogen atom or an oxygen atom is considerably greater than the bond energy between a carbon atom and a hetero atom. Further, the intermolecular force of the organic silicone compound is smaller than that of the similar carbon compound. Therefore, a material comprising an organic silicone compound is easily influenced by the properties of a molecule of the silicone compound.
Under such circumstances, the synthesis of an organic silicone compound having a quaternary salt structure has not been actively conducted although such a silicone compound is considered to show interesting physical properties. More specifically, the molecular polarization of the silicone compound in the form of a quaternary salt is great because there are a substituent for silicone and a quaternary base in the molecule thereof; and further, the former is hydrophobic, whereas the latter is hydrophilic.
To make a copy by the electrophotographic process, there is conventionally well known a method of uniformly charging a photoconductor, exposing the thus charged photoconductor to light images based on an original document to dissipate the electric charge of the light-exposed areas on the photoconductor, thereby forming latent electrostatic images corresponding to the light images, and then developing the latent electrostatic images into visible images by a two-component dry developer comprising carrier particles and toner particles. In such a two-component dry developer fine toner particles are held on the surface of a relatively large carrier particle triboelectrically, that is, by means of electrostatic force generated by the friction between both particles. When the carrier particle covered with toner particles is brought into immediate proximity of the latent electrostatic image, the electrostatic forces of the latent electrostatic image attracting the toner particles overcome the carrier-toner bond, and the toner particles are attracted to the latent electrostatic image and deposited thereon. Thus, latent electrostatic images can be developed into visible images.
The requirements for such toner particles are excellent chargeability, minimum moisture-absorption characteristics, good stability for an extended period of time, and proper fluidity. Of these requirements, the chargeability, the moisture-absorption characteristics and the stability are much influenced by a charge controlling agent contained in the toner particles.
The charge controlling agent, which is added to a formulation for a toner in order to impart a required charge quantity to the toner, is one of the very important materials constituting the toner. The polarity of toner is generally determined depending on the desired properties of a developer to be obtained, and a proper charge controlling agent is thus selected.
Examples of the conventional charge controlling agent capable of negatively charging the toner include metal complexes such as Cr- and Co-complexes (as disclosed in Japanese Laid-Open Patent Applications 61-217061 and 63-216061), nitrohumic acids (as disclosed in Japanese Laid-Open Patent Application 50-133838), and phthalocyanine pigment (as disclosed in Japanese Laid-Open Patent Application 60-258560).
Examples of the conventional charge controlling agent capable of positively charging the toner include salts of a nigrosine dye (as disclosed in Japanese Laid-Open Patent Application 56-22441), a variety of quaternary ammonium salts (as disclosed in Japanese Laid-Open Patent Application 59-136747), and imidazole derivatives (as disclosed in Japanese Laid-Open Patent Application 3-72373).
The conventional toners employing the above-mentioned conventional charge controlling agents did not meet all of the above-mentioned requirements such as excellent chargeability, minimum moisture-absorption characteristics and good stability. In addition, the compatibility of each conventional charge controlling agent with a binder agent is poor.
For instance, although a toner comprising a conventional nigrosine dye as the positively chargeable charge controlling agent shows a relatively high chargeability, the adhesion of the toner to a base material such as a sheet of paper is very poor. Further, the conventional nigrosine dye assumes a black color, so that the application of such a charge controlling agent is limited in view of the hue of a toner to be produced. Some toners employing the conventional quaternary ammonium salts as the charge controlling agents have the shortcoming that the moisture absorption is considerably high, so that the stability of the toners cannot be ensured for an extended period of time, and it becomes difficult to repeatedly obtain images using such toners.